1. Field of the Invention
This invention relates to a control apparatus and a control method for an internal combustion engine.
2. Description of Related Art
There is a possibility that the characteristics of a throttle valve may vary with temporal change due to, for example, the accumulation of deposits. In other words, even at the same opening degree, the opening area becomes narrower as the accumulation of deposits progresses, and the intake air amount may be reduced.
In the control apparatus for an internal combustion engine described in Japanese Patent Application Publication No. 2012-17679 A (JP 2012-17679 A), the rate of change in the flow volume in each opening degree region which is divided in accordance with the opening degree of the throttle valve is learnt, so as to correspond to such temporal change in the characteristics of the throttle valve. The rate of change in the flow volume is an indicator which represents the extent of divergence between a reference value of the intake air volume and the value of the intake air volume which has actually been detected by an air flow meter. By using this change in the flow volume to correct the reference value of the intake air volume, then it is possible to determine the present characteristics of the throttle valve after temporal change has progressed.
JP 2012-17679 A indicates previously storing the initial value of the rate of change of the flow volume in the control apparatus for an internal combustion engine, and to use this initial value in an unlearnt opening degree region—an opening degree region for which learning has not been performed. JP 2012-17679 A indicates that, when there is an unlearnt opening degree region to the lower side of a learnt opening degree region, then a value equal to the learnt value in the opening degree region nearest to the unlearnt opening degree region, of the learnt opening degree regions, is used as a learnt value for this unlearnt opening degree region.